Luminescence and energy transfer performances of Tb3+/Mn4+ co-doped Sr2LuTaO6 double-perovskite phosphors for a highly sensitive optical thermometer

A series of Tb3+/Mn4+ co-doped double-perovskite oxides Sr2LuTaO6 (SLT) phosphors are synthesized by a solid-state method. The results of structural characterization prove that the Tb3+ and Mn4+ ions are successfully doped into the SLT host. The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Sr2LuTaO6:Tb3+, Sr2LuTaO6:Mn4+ and Sr2LuTaO6:Tb3+/Mn4+ are illustrated in detail. Under ultraviolet (UV) excitation, bright green and red lights are obtained from the Sr2LuTaO6:Tb3+/Mn4+ phosphor. In particular, the emission intensity of Tb3+ ions in Sr2LuTaO6:Tb3+/Mn4+ is enhanced by the energy transfer (ET) process from Mn4+ to Tb3+. The thermal enhancement of Tb3+ ion radiation in Sr2LuTaO6:Tb3+/Mn4+ also proves the ET process (Mn4+ → Tb3+). In addition, the thermal enhancement of Tb3+ ion radiation and the thermal quenching of Mn4+ ion radiation in the Sr2LuTaO6:Tb3+/Mn4+ system can be applied to develop optical thermometry based on luminescence intensity ratio (LIR) technology. Therefore, the LIRs of Mn4+ (2Eg → 4A2g) and Tb3+ (5D4 → 7F5,4) are investigated in the temperature range from 313 to 573 K. The absolute sensitivity (Sa) and relative sensitivity (Sr) of the Sr2LuTaO6:Tb3+/Mn4+ phosphor are calculated. The maximum values of Sa and Sr are obtained from the LIR of Tb3+: 5D4 → 7F4 (570-599 nm) and Mn4+: 2Eg → 4A2g (625-705 nm). The maximum Sa is 10.18% K-1 at 543 K, and the maximum value of Sr reaches 1.98% K-1 at 543 K. These results confirm that the ET process from Mn4+ to Tb3+ contributes to increasing the temperature measuring sensitivity of the Sr2LuTaO6:Tb3+/Mn4+ phosphor. Therefore, the Sr2LuTaO6:Mn4+/Tb3+ phosphor has prospective potential in optical thermometry and provides advantageous guidance for designing high-sensitivity optical thermometers.